Schottky barrier devices are widely used in many consumer, commercial and other applications. A Schottky barrier is a potential barrier formed at a metal-semiconductor junction, which has rectifying characteristics. Many Schottky barrier devices use wide bandgap semiconductors, such as silicon carbide, gallium nitride and/or gallium arsenide, which may be used for high power, high temperature and/or microwave applications. Semiconductor Schottky barrier devices include Schottky diodes, High Electron Mobility Transistors (HEMTs) and MEtal Semiconductor Field Effect Transistors (MESFETs). A HEMT is a field effect transistor that incorporates a junction between two materials with different bandgaps (i.e., a heterojunction) as the channel, instead of a doped region, as is generally the case in integrated circuit field effect transistors. A Schottky barrier gate is used to control a two-dimensional electron gas (2DEG) between a source region and a drain region. In a MESFET, a Schottky barrier gate is used to control conduction in a doped channel that is formed between source and drain regions.
The length of the Schottky gate contact of the semiconductor device may directly impact the operation speed and performance of the semiconductor device. Conventional methods of forming these gates typically consist of photoresist patterning followed by an etch of a dielectric down to the surface of the semiconductor. The gate length is defined by the dimension of the dielectric opening. The dielectric profile can be adjusted by adjusting the photoresist profile, which can vary from straight, perpendicular to slightly sloped. The slope is commonly achieved through a photoresist reflow step that consists of baking beyond the glass transition temperature. This process may be difficult to control and may not provide the variation requested by customers for their devices.